In a typical light-scattering smoke detector, infrared rays are emitted into a smoke detecting chamber. When smoke enters the smoke chamber, the infrared rays are scattered by the smoke and detected by a light receiving device, such as a photodiode. It is preferable to have a compact smoke detector for aesthetic reasons, so as not to prominently protrude, for example, from a building ceiling.
It is important that the smoke chamber have a large enough opening for allowing smoke to easily flow therein, while excluding ambient light which can initiate nuisance alarms.
Numerous designs have been previously proposed to accomplish the foregoing, for example, as disclosed in U.S. Pat. Nos. 4,315,158 to Kakigi et al. and 5,670,947 to Nagashima. Typical designs include a series of labyrinth members which form the wall around the smoke chamber and which allow the smoke into the chamber while excluding ambient light.
Prior art light-scattering smoke detectors have failed to provide a relatively compact smoke chamber which excludes ambient light even when the components that form the smoke chamber are slightly misaligned. Accordingly, a smoke detecting chamber for use in a light-scattering type smoke detector is provided which includes a chamber cover that forms one side of the smoke detecting chamber. The chamber cover includes a plurality of first baffles that prevent external light from entering the smoke chamber. The smoke detector further includes a chamber base that forms another side of the smoke detecting chamber, the chamber base including a plurality of second baffles that intermesh with the first baffles when the smoke detecting chamber is formed.
A smoke detector is also provided which includes a printed circuit board having a first side and a second side with electronic components positioned on the first side of the board. A can for isolating the electronic components from external radio frequency emissions covers the electronic components on the first side of the board. A smoke detecting chamber is formed on the second side of the board by a chamber cover and a chamber base. An optical bench is disposed between the second side of the board and the smoke detecting chamber. The optical bench holds an emitting device, that emits radiation into the smoke chamber, and a sensing device that senses radiation from the emitting device when smoke fills the smoke detecting chamber.
In alternative embodiments, a smoke detector is provided which includes a printed circuit board having a first side and a second side. A smoke detecting chamber, which can be formed with a chamber cover and a chamber base, is positioned on the second side of the board. An emitting device is configured to emit radiation into the smoke chamber. A sensing device, positioned on the first side of the board, senses radiation from the emitting device when smoke fills the smoke detecting chamber. The smoke detector further includes a lens, combined with a reflecting element such as a prism, that redirects radiation through an aperture in the board to the sensing device. An optical bench preferably holds the emitting device and the lens.
In another embodiment, a smoke detector is provided which includes a smoke detecting chamber, an emitting device that emits radiation into the smoke chamber, and a sensing device that senses radiation from the emitting device when smoke fills the smoke detecting chamber. A first reflecting surface is provided in the smoke detecting chamber wherein at least a portion of the reflecting surface is directly impinged by the radiation from the emitting device. A second reflecting surface in the smoke detecting chamber is configured to reflect radiation reflected by the first reflecting surface toward the sensing device. The reflectors provide a clean air background signal.
Preferably, the smoke chamber is formed by a chamber cover and a chamber base and the first and second reflecting surfaces extend from the chamber cover. The emitting device and the sensing device include optical axes which preferably intersect in the range of between about 30 and 40 degrees, preferably about 37.5 degrees.